U.S. patent application number 14/005709 was filed with the patent office on 2014-02-20 for method of determining correction amount of opening degree of egr valve, method of controlling opening degree of egr valve, and engine.
This patent application is currently assigned to Yanmar Co., Ltd.. The applicant listed for this patent is Tomohiro Fukuda, Atsushi Ueta. Invention is credited to Tomohiro Fukuda, Atsushi Ueta.
Application Number | 20140048051 14/005709 |
Document ID | / |
Family ID | 46879371 |
Filed Date | 2014-02-20 |
United States Patent
Application |
20140048051 |
Kind Code |
A1 |
Fukuda; Tomohiro ; et
al. |
February 20, 2014 |
Method of Determining Correction Amount of Opening Degree of EGR
Valve, Method of Controlling Opening Degree of EGR Valve, and
Engine
Abstract
A method determines a correction amount of an EGR valve opening
degree. A basic correction amount map is generated indicating a
correlation between rotating speed, load factor, and the correction
amount, while the opening degree is maintained at a reference
opening degree and the EGR rate is maintained at a target EGR rate,
based on correction amounts obtained for mutually different
individual combinations of the rotating speed and the load factor.
Estimated values of the correction amounts not contained in the
basic map are acquired by estimating the distribution of the
amounts not in the basic map based on a distribution trend. An
extended correction amount map is generated indicating a
correlation between the estimated values of the rotating speed, the
load factor, and the correction amount while the opening degree is
maintained at a reference opening degree and the EGR rate is
maintained at a target rate.
Inventors: |
Fukuda; Tomohiro;
(Osaka-shi, JP) ; Ueta; Atsushi; (Osaka-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Fukuda; Tomohiro
Ueta; Atsushi |
Osaka-shi
Osaka-shi |
|
JP
JP |
|
|
Assignee: |
Yanmar Co., Ltd.
Osaka-shi, Osaka
JP
|
Family ID: |
46879371 |
Appl. No.: |
14/005709 |
Filed: |
March 16, 2012 |
PCT Filed: |
March 16, 2012 |
PCT NO: |
PCT/JP2012/056914 |
371 Date: |
October 11, 2013 |
Current U.S.
Class: |
123/568.21 |
Current CPC
Class: |
F02M 26/39 20160201;
F02M 26/05 20160201; F02M 26/48 20160201; Y02T 10/47 20130101; F02M
26/40 20160201; Y02T 10/40 20130101; F02D 41/0077 20130101; F02D
41/0072 20130101; F02D 41/0052 20130101 |
Class at
Publication: |
123/568.21 |
International
Class: |
F02M 25/07 20060101
F02M025/07 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 18, 2011 |
JP |
2011/060284 |
Claims
1. A method of determining a correction amount of an opening degree
of an EGR valve, the method determining the correction amount for
correcting the opening degree to a target opening degree
corresponding to a differential pressure between an exhaust
pressure and an intake pressure such that an EGR rate is maintained
at a predetermined target EGR rate, the EGR rate being specified on
the basis of the differential pressure, the opening degree, and the
air intake amount, even when the differential pressure changes, the
method comprises: a differential pressure map generating step of
generating a differential pressure map indicating a correlation
between a rotating speed of an engine, a load factor of the engine,
and the differential pressure while the opening degree is
maintained at a reference opening degree, the differential pressure
map being set for each of a plurality of mutually different
reference opening degrees; a correction amount calculating step of
calculating the correction amount equal to a difference between the
target opening degree and the reference opening degree for each of
mutually different combinations of the rotating speed and the load
factor, by utilizing that the target opening degree is specified on
the basis of the target EGR rate, the differential pressure, and
the air intake amount, and that the differential pressure is
specified on the basis of the rotating speed and the load factor; a
basic correction amount map generating step of generating a basic
correction amount map indicating a correlation between the rotating
speed, the load factor, and the correction amount while the opening
degree is maintained at the reference opening degree and the EGR
rate is maintained at the target EGR rate, on the basis of the
correction amount obtained for each of mutually different
combinations of the rotating speed and the load factor; and an
extended correction amount map generating step of acquiring
estimated values of correction amounts not contained in the basic
correction amount map, by estimating the distribution of the
correction amounts not contained in the basic correction amount
map, on the basis of a trend in the distribution of the correction
amounts contained in the basic correction amount map, and
generating an extended correction amount map indicating a
correlation between the rotating speed, the load factor, and the
estimated value of the correction amount, while the opening degree
is maintained at the reference opening degree and the EGR rate is
maintained at the target EGR rate.
2. The method of determining the correction amount of the opening
degree of the EGR valve according to claim 1, wherein the
correction amount contained in the basic correction amount map is
the correction amount corresponding to each combination of the
rotating speed and the load factor, while the differential pressure
is zero or positive, and wherein the correction amount contained in
the extended correction amount map is the correction amount
corresponding to each combination of the rotating speed and the
load factor, while the differential pressure is negative.
3. A method of controlling the opening degree of the EGR valve,
comprising: a rotating speed detection step of detecting the
rotating speed; a load factor detection step of detecting the load
factor; an air intake amount detection step of detecting the air
intake amount; a correction amount specifying step of specifying
the correction amount corresponding to the reference opening
degree, the rotating speed, and the load factor, on the basis of a
plurality of the basic correction amount maps and the extended
correction amount maps obtained by the method of determining the
correction amount of the opening degree of the EGR valve according
to claim 1; and an opening degree controlling step of controlling
the opening degree to the target opening degree corresponding to
the correction amount and the reference opening degree having been
specified.
4. An engine comprising: a rotating speed detection section for
detecting the rotating speed; a load factor detection section for
detecting the load factor; an air intake amount detection section
for detecting the air intake amount; a correction amount map
specifying section for specifying the correction amount
corresponding to the reference opening degree, the rotating speed,
and the load factor, on the basis of a plurality of the basic
correction amount maps and the extended correction amount maps
obtained by the method of determining the correction amount of the
opening degree of the EGR valve according to claim 1; and a
correction amount specifying section specifying the correction
amount corresponding to the reference opening degree, the rotating
speed, and the load factor, on the basis of the correction amount
map having been specified; and an opening degree control section
for controlling the opening degree to the target opening degree
corresponding to the correction amount and the reference opening
degree having been specified.
5. A method of controlling the opening degree of the EGR valve,
comprising: a rotating speed detection step of detecting the
rotating speed; a load factor detection step of detecting the load
factor; an air intake amount detection step of detecting the air
intake amount; a correction amount specifying step of specifying
the correction amount corresponding to the reference opening
degree, the rotating speed, and the load factor, on the basis of a
plurality of the basic correction amount maps and the extended
correction amount maps obtained by the method of determining the
correction amount of the opening degree of the EGR valve according
to claim 2; and an opening degree controlling step of controlling
the opening degree to the target opening degree corresponding to
the correction amount and the reference opening degree having been
specified.
6. An engine comprising: a rotating speed detection section for
detecting the rotating speed; a load factor detection section for
detecting the load factor; an air intake amount detection section
for detecting the air intake amount; a correction amount map
specifying section for specifying the correction amount
corresponding to the reference opening degree, the rotating speed,
and the load factor, on the basis of a plurality of the basic
correction amount maps and the extended correction amount maps
obtained by the method of determining the correction amount of the
opening degree of the EGR valve according to claim 2; and a
correction amount specifying section specifying the correction
amount corresponding to the reference opening degree, the rotating
speed, and the load factor, on the basis of the correction amount
map having been specified; and an opening degree control section
for controlling the opening degree to the target opening degree
corresponding to the correction amount and the reference opening
degree having been specified.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method of determining a
correction amount of an opening degree of an EGR valve, the method
determining the correction amount for correcting the opening degree
to a target opening degree corresponding to a differential pressure
between an exhaust pressure and an intake pressure such that an EGR
rate is maintained at a predetermined target EGR rate, the opening
degree, and the air intake amount, even when the differential
pressure changes.
BACKGROUND ART
[0002] In an EGR apparatus, an intake pipe and an exhaust pipe are
linked through an EGR pipe so that exhaust gas is supplied through
the EGR pipe to the intake pipe. Further, in the inside of the EGR
pipe, an EGR valve is provided for controlling the flow rate of the
EGR gas (the exhaust gas flowing through the intake pipe).
[0003] In a technique investigated presently, a differential
pressure between the exhaust pressure and the intake pressure is
detected and then the opening degree of the EGR valve is corrected
in accordance with the differential pressure so that changing of
the EGR rate caused by changing of the differential pressure is
suppressed. An example of such a technique is, for example, a
technique described in Patent Document 1 by the present
applicant.
[0004] Here, the EGR rate, the EGR gas amount, the air intake
amount, the differential pressure, and the opening degree satisfy
the following relations shown in Formulas (1) and (2).
EGR rate=EGR gas amount/(air intake amount+EGR gas amount) (1)
EGR Gas Amount=Proportionality Constant*Differential
Pressure*Opening Degree Of an EGR Valve (2)
[0005] The EGR rate is specified by detecting the air intake
amount, the differential pressure, and the opening degree of the
EGR valve. Therefore, when the opening degree is changed in
accordance with changing of the differential pressure, the EGR rate
can be maintained at a predetermined target rate.
CITATION LIST
Patent Literature
[0006] Patent Document 1 Japanese Patent Application No.
2010-169472
SUMMARY OF INVENTION
Technical Problem
[0007] As described above, the EGR gas amount is obtained as a
value proportional to the product of the differential pressure and
the opening degree of the EGR valve. Therefore, when the average
exhaust pressure is higher than the average intake pressure and
hence the differential pressure has a negative value, the EGR gas
amount cannot be obtained.
[0008] Since the exhaust gas has a higher temperature than the
intake air, in general, the exhaust pressure is higher than the
intake pressure. Therefore, the intake air does not flow backward
from the intake pipe to the exhaust pipe. On the other hand, in an
engine with a turbocharger, the intake pressure is increased. This
causes condition that the intake pressure is higher than the
exhaust pressure. Here, in accurate description, the intake
pressure and the exhaust pressure respectively indicate the average
intake pressure and the average exhaust pressure which are averaged
values of the intake pressure and the exhaust pressure per unit
time. The intake pressure and the exhaust pressure have ripples in
association with the opening and closing of the intake valve and
the exhaust valve. Therefore, even when the average intake pressure
is higher than the average exhaust pressure, the exhaust pressure
becomes higher than the intake pressure momentarily, in some cases.
Accordingly, even in a case that the intake pressure is higher than
the exhaust pressure, EGR (exhaust gas recirculation) can be
implemented. Here, for the purpose of preventing the intake air
from flowing into the exhaust pipe, a reed valve that opens only
when the exhaust pressure is higher than the intake pressure is
provided in the inside of the EGR pipe.
[0009] That is, in the above-mentioned determination Formula (2)
for the EGR gas amount, it is premised that a constant differential
pressure always acts in the EGR pipe and is not premised that the
EGR gas flows through the reed valve into the intake pipe owing to
the ripples in the intake pressure and the exhaust pressure.
Therefore, when the average exhaust pressure is higher than the
average intake pressure, a correction amount used for correcting
the opening degree of the EGR valve cannot be specified. Since the
correction amount cannot be specified, correcting the opening
degree of the EGR valve such that changing of the EGR rate caused
by changing of the differential pressure should be suppressed
cannot be performed.
[0010] Therefore, the present invention provides a method of
determining a correction amount of the opening degree of the EGR
valve, in which even in operating condition where a correction
value is not obtained like in operating condition where the average
exhaust pressure is higher than the average intake pressure, a
correction amount of the opening degree of an EGR valve can be
determined such that the EGR rate is maintained at constant.
Solution to Problem
[0011] The present invention provides a method of determining a
correction amount of an opening degree of an EGR valve, the method
determining the correction amount for correcting the opening degree
to a target opening degree corresponding to a differential pressure
between an exhaust pressure and an intake pressure such that an EGR
rate is maintained at a predetermined target EGR rate, the EGR rate
being specified on the basis of the differential pressure, the
opening degree, and the air intake amount, even when the
differential pressure changes, the method comprises: a differential
pressure map generating step of generating a differential pressure
map indicating a correlation between a rotating speed of an engine,
a load factor of the engine, and the differential pressure while
the opening degree is maintained at a reference opening degree, the
differential pressure map being set for each of a plurality of
mutually different reference opening degrees; a correction amount
calculating step of calculating the correction amount equal to a
difference between the target opening degree and the reference
opening degree for each of mutually different combinations of the
rotating speed and the load factor, by utilizing that the target
opening degree is specified on the basis of the target EGR rate,
the differential pressure, and the air intake amount, and that the
differential pressure is specified on the basis of the rotating
speed and the load factor; a basic correction amount map generating
step of generating a basic correction amount map indicating a
correlation between the rotating speed, the load factor, and the
correction amount while the opening degree is maintained at the
reference opening degree and the EGR rate is maintained at the
target EGR rate, on the basis of the correction amount obtained for
each of mutually different combinations of the rotating speed and
the load factor; and an extended correction amount map generating
step of acquiring estimated values of correction amounts not
contained in the basic correction amount map, by estimating the
distribution of the correction amounts not contained in the basic
correction amount map, on the basis of a trend in the distribution
of the correction amounts contained in the basic correction amount
map, and generating an extended correction amount map indicating a
correlation between the rotating speed, the load factor, and the
estimated value of the correction amount, while the opening degree
is maintained at the reference opening degree and the EGR rate is
maintained at the target EGR rate.
[0012] Preferably, the correction amount contained in the basic
correction amount map is the correction amount corresponding to
each combination of the rotating speed and the load factor, while
the differential pressure is zero or positive, and the correction
amount contained in the extended correction amount map is the
correction amount corresponding to each combination of the rotating
speed and the load factor, while the differential pressure is
negative.
[0013] The present invention provides a method of controlling the
opening degree of the EGR valve, comprising: a rotating speed
detection step of detecting the rotating speed; a load factor
detection step of detecting the load factor; an air intake amount
detection step of detecting the air intake amount; a correction
amount specifying step of specifying the correction amount
corresponding to the reference opening degree, the rotating speed,
and the load factor, on the basis of a plurality of the basic
correction amount maps and the extended correction amount maps
obtained by the method of determining the correction amount of the
opening degree of the EGR valve; and an opening degree controlling
step of controlling the opening degree to the target opening degree
corresponding to the correction amount and the reference opening
degree having been specified.
[0014] The present invention provides an engine comprising: a
rotating speed detection section for detecting the rotating speed;
a load factor detection section for detecting the load factor; an
air intake amount detection section for detecting the air intake
amount; a correction amount map specifying section for specifying
the correction amount corresponding to the reference opening
degree, the rotating speed, and the load factor, on the basis of a
plurality of the basic correction amount maps and the extended
correction amount maps obtained by the method of determining the
correction amount of the opening degree of the EGR valve; and a
correction amount specifying section specifying the correction
amount corresponding to the reference opening degree, the rotating
speed, and the load factor, on the basis of the correction amount
map having been specified; and an opening degree control section
for controlling the opening degree to the target opening degree
corresponding to the correction amount and the reference opening
degree having been specified.
Advantageous Effects of Invention
[0015] The method of determining the correction amount of opening
degree of the EGR valve according to the present invention can
specify the correction amount on the basis of estimated values of
the correction values. Therefore, the method can determine the
correction amount of the opening degree of the EGR valve such that
the EGR rate is maintained at constant, even in operating condition
where the correction values are not obtained like in operating
condition where the average exhaust pressure is higher than the
average intake pressure.
[0016] The method of controlling the opening degree of the EGR
valve and the engine according to the present invention can correct
the opening degree of the EGR valve such that the EGR rate is
maintained at constant, even in operating condition where the
correction values are not obtained like in operating condition
where the average exhaust pressure is higher than the average
intake pressure.
BRIEF DESCRIPTION OF DRAWINGS
[0017] FIG. 1 is a configuration diagram of an engine 1.
[0018] FIG. 2 is a diagram showing a differential pressure map
indicating a correlation between a rotating speed, a load factor,
and a differential pressure while an opening degree is maintained
at an n-th reference opening degree.
[0019] FIG. 3 is a diagram showing a basic correction amount map
indicating a correlation between a rotating speed, a load factor,
and a correction amount while an opening degree is maintained at an
n-th reference opening degree and an EGR rate is maintained at a
target EGR rate.
[0020] FIG. 4 is a diagram showing a basic correction amount map
indicating a correlation between a rotating speed, a load factor,
and a correction amount while an opening degree is maintained at an
n-th reference opening degree and an EGR rate is maintained at a
target EGR rate.
[0021] FIG. 5 is a block diagram showing a configuration related to
control of an opening degree.
DESCRIPTION OF EMBODIMENTS
[0022] FIG. 1 is a configuration diagram of an engine 1. The engine
1 includes a cylinder head 2, a cylinder block 3, a plurality of
cylinders 4, a crankshaft 5, an intake pipe 6, an exhaust pipe 7,
an exhaust gas recirculation apparatus (an EGR apparatus,
hereinafter) 8, a turbocharger 9, and a common rail type fuel
injection apparatus (a common rail, hereinafter) 10.
[0023] The EGR apparatus 8 includes an EGR pipe 11, an EGR valve
12, and a reed valve 13. The EGR pipe 11 establishes fluid
communication between the exhaust pipe 7 and the intake pipe 6. The
EGR valve 12 and the reed valve 13 are arranged in the inside of
the EGR pipe 11. The EGR valve 12 changes the flow rate of the
exhaust gas passing through the inside of the EGR pipe 11, by
changing an opening degree thereof. In the inside of the EGR pipe
11, the reed valve 13 permits only the flow of the exhaust gas from
the exhaust pipe 7 to the intake pipe 6 and inhibits the flow of
the exhaust gas from the intake pipe 6 to the exhaust pipe 7. In
the flowing description, the exhaust gas flowing from the exhaust
pipe 7 through the EGR pipe 11 to the intake pipe 6 is referred to
as EGR gas.
[0024] Further, as a configuration for control, the engine 1
includes a control unit 20, a rotating speed sensor 21, and an air
flow meter 22. The rotating speed sensor 21 detects the rotating
speed of the crankshaft 5. The air flow meter 22 detects the mixed
intake amount passing through the intake pipe 6. Here, the air flow
meter 22 is arranged in the downstream of the outlet of the EGR
pipe 11 in the intake pipe 6. Therefore, the mixed intake amount
indicates the amount of gas where the EGR gas has been mixed into
the outside air. That is, the mixed intake amount indicates the
total amount of the air intake amount and the EGR gas amount. The
control unit 20 is capable of acquiring detection information of
the rotating speed sensor 21 and the air flow meter 22. Further,
the control unit 20 controls the common rail 10 and the EGR valve
12.
[0025] The control unit 20 is configured to control the opening
degree of the EGR valve 12 to a target opening degree corresponding
to the differential pressure such that the EGR rate is maintained
at a predetermined target rate, even when the differential pressure
between the exhaust pressure and the intake pressure changes. The
control unit 20 stores a correction amount map CM used for
correcting the opening degree of the EGR valve 12 to the target
opening degree. The correction amount map CM is generated by a
later-described method of determining a correction amount of the
opening degree of the EGR valve.
[0026] The method of determining a correction amount of the opening
degree of the EGR valve is described below with reference to FIGS.
2 to 4. This correction amount determination method includes a
differential pressure map generating step, a correction amount
calculating step, a basic correction amount map generating step,
and an extended correction amount map generating step.
[0027] The correction amount determination method determines a
correction amount used for obtaining a target opening degree for
realizing a target EGR rate such that the EGR rate is maintained at
the predetermined target EGR rate. Here, the correction amount
indicates the difference between the target opening degree and a
predetermined reference opening degree. Further, the EGR rate to be
specified on the basis of the differential pressure, the opening
degree of the EGR valve, and the air intake amount varies depending
on the magnitude of the reference opening degree. Since the exhaust
pressure varies depending on the EGR rate, the differential
pressure also varies and hence the correction amount to be set up
depending on the differential pressure also varies. That is, the
magnitude of the correction amount varies depending not only on the
magnitude of the target EGR rate but also on the magnitude of the
reference opening degree. The correction amount is set up for each
reference opening degree. Therefore, when the number of mutually
different reference opening degrees is increased, precision in the
correction is improved. Nevertheless, since a large amount of data
of correction amount is set up for each reference opening degree,
the amount of data to be stored in the control unit 20 increases.
Therefore, the number of reference opening degrees is limited to a
certain value.
[0028] In the present embodiment, a first to a sixth reference
opening degree (%) are set up as predetermined reference opening
degrees. The values are 0%, 20%, 40%, 60%, 80%, and 100%. An n-th
reference opening degree indicates any one of the first to the
sixth reference opening degree. A differential pressure map and a
correction amount map CM described later are set up for each
reference opening degree.
Differential Pressure Map Generating Step
[0029] FIG. 2 is a diagram showing a differential pressure map
indicating a correlation between a rotating speed, a load factor,
and a differential pressure while an opening degree is maintained
at an n-th reference opening degree. In FIG. 2, the horizontal axis
indicates the rotating speed of the engine 1. The vertical axis
indicates the load factor of the engine 1. The load factor
indicates a ratio concerning the fuel injection amount per one
revolution of the engine 1 and is defined as the ratio of the
present fuel injection amount to the maximum fuel injection amount
that can be set up. Here, the engine 1 is controlled such that the
rotating speed is maintained at constant. Therefore, the fuel
injection amount increases with increasing load on the engine 1.
The differential pressure indicates a pressure difference obtained
by subtracting the intake pressure from the exhaust pressure.
[0030] Here, in the present specification, the intake pressure and
the exhaust pressure respectively indicate the average intake
pressure and the average exhaust pressure which are averaged values
of the intake pressure and the exhaust pressure per unit time.
[0031] The differential pressure map generating step is a step of
generating the differential pressure map shown in FIG. 2. In FIG.
2, for each of mutually different combinations of the rotating
speed and the load factor, a differential pressure corresponding to
the rotating speed and the load factor is obtained. In FIG. 2, each
differential pressure data set SD indicates a set of data
consisting of the rotating speed, the load factor, and the
differential pressure, which is specified by one of mutually
different combinations of the rotating speed and the load factor.
Here, in accordance with the characteristics of the engine 1, the
differential pressure corresponding to the rotating speed and the
load factor can be detected experimentally.
[0032] In FIG. 2, a plurality of equi-pressure lines are drawn.
Each equi-pressure line is a set of coordinates (a rotating speed
and a load factor) where the differential pressure is the same on
the differential pressure map. The magnitude of differential
pressure on each equi-pressure line is, for example, any one of
-1D, 0, and +1D to +7D. The symbol (D) indicates the absolute value
of a differential pressure of certain value. The sign (+) or (-)
indicates whether the differential pressure is positive or
negative. The numeric character (2) or the like added to the symbol
(D) indicates a ratio to the differential pressure of certain
value. The magnitude of a differential pressure of +4D is twice the
differential pressure of +2D.
[0033] A plurality of equi-pressure lines indicate a trend in the
distribution of differential pressure. The differential pressure is
increasing from the upper left region toward the right-hand side
region in FIG. 2. The upper left region in FIG. 2 is a negative
pressure region Am where the differential pressure is negative. The
other region is a positive pressure region Ap where the
differential pressure is positive.
Correction Amount Calculating Step
[0034] The correction amount calculating step is a step of
calculating a correction amount that is equal to the difference
between the target opening degree and the reference opening degree,
for each of mutually different combinations of the rotating speed
and the load factor. As shown in Formula (3), the correction amount
is the difference between the target opening degree and the
reference opening degree. That is, as shown in Formula (4), the
target opening degree serving as the opening degree after
correction is the sum of the reference opening degree and the
correction amount.
Correction Amount=Target Opening Degree-Reference Opening Degree
(3)
Target Opening Degree (Opening Degree After Correction)=Reference
Opening Degree+Correction Amount (4)
[0035] Here, the EGR rate, the EGR gas amount, the air intake
amount, the differential pressure, and the opening degree satisfy
the following relations shown in Formulas (1) and (2).
EGR Rate=EGR Gas Amount/(Air Intake Amount+EGR Gas Amount) (1)
EGR Gas Amount=Proportionality Constant*Differential
Pressure*Opening Degree of EGR Valve (2)
[0036] Since the opening degree is specified on the basis of the
EGR rate, the differential pressure, and the air intake amount, the
target opening degree is specified on the basis of the target EGR
rate, the differential pressure, and the air intake amount.
Therefore, the correction amount equal to the difference between
the target opening degree and the reference opening degree is
specified on the basis of the reference opening degree, the target
EGR rate, the differential pressure, and the air intake amount.
Further, as shown in the correction map in FIG. 2, the differential
pressure is specified on the basis of the rotating speed and the
load factor. Therefore, the correction amount is specified on the
basis of the reference opening degree, the target EGR rate, the
rotating speed, the load factor, and the air intake amount. The
reference opening degree, the target EGR rate, and the air intake
amount are constants specified depending on the operating condition
and the like. The rotating speed, the load factor, and the
correction amount are variables. Therefore, in the correction
amount calculating step, a correction amount is obtained for each
of mutually different combinations of the rotating speed and the
load factor.
[0037] Nevertheless, when the differential pressure is negative,
the correction amount cannot be specified on the basis of the
reference opening degree, the target EGR rate, the rotating speed,
the load factor, and the air intake amount. Therefore, the
correction amount cannot be obtained from the combinations of the
rotating speed and the load factor contained in the negative
pressure region Am.
Basic Correction Amount Map Generating Step
[0038] The basic correction amount map generating step is a step of
generating a basic correction amount map BCM shown in FIG. 3, for
example. The basic correction amount map BCM indicates a
correlation between the rotating speed, the load factor, and the
correction amount while the EGR rate is maintained at the target
EGR rate. The basic correction amount map BCM is generated on the
basis of the correction amount obtained for each of mutually
different combinations of the rotating speed and the load factor.
Further, one of mutually different basic correction amount maps BCM
is generated for each of mutually different reference opening
degrees.
[0039] FIG. 3 is a diagram showing a basic correction amount map
indicating a correlation between a rotating speed, a load factor,
and a correction amount while an opening degree is maintained at an
n-th reference opening degree and an EGR rate is maintained at a
target EGR rate. In FIG. 3, the horizontal axis indicates the
rotating speed. The vertical axis indicates the load factor. In
FIG. 3, for each of mutually different combinations of the rotating
speed and the load factor, a correction amount is shown that
corresponds to the rotating speed and the load factor. In FIG. 3,
each correction amount data set SC indicates a set of data
consisting of the rotating speed, the load factor, and the
correction amount, which is specified by one of mutually different
combinations of the rotating speed and the load factor.
[0040] In FIG. 3, isopleth lines for a plurality of correction
amounts are drawn. Each isopleth line is a set of coordinates (a
rotating speed and a load factor) where the correction amount is
the same on the basic correction amount map BCM. The magnitude of
correction amount on each isopleth line is, for example, any one of
0.2C, 0.4C, and 0.6C to 1.6C. Here, the magnitude of correction
amount on the isopleth line is set up as an equal interval of 0.2C.
The symbol (C) indicates a correction amount of certain value. The
numeric character (2) or the like added to the symbol (C) indicates
a ratio to the correction amount of certain value. The magnitude of
a correction amount of 0.4C is 0.4 times the correction amount of
1.0C. That is, an arbitrary correction amount is adopted as a
reference and then other correction amount is expressed by using a
ratio to the reference correction amount.
[0041] A plurality of isopleth lines indicate a trend in the
distribution of correction amounts. The correction amount is
increasing from the upper region toward the lower region in FIG.
3.
[0042] The differential pressure map in FIG. 2 and the basic
correction amount map BCM in FIG. 3 include the rotating speed and
the load factor as elements. Therefore, basically, the differential
pressure map and the basic correction amount map BCM correspond to
each other. Nevertheless, as described above, the correction amount
is not obtained in the negative pressure region Am. Therefore, the
basic correction amount map BCM in FIG. 3 does not contain an
uncorrectable region Anc corresponding to the negative pressure
region Am. The basic correction amount map BCM in FIG. 3 lacks the
upper left region in comparison with the differential pressure map
in FIG. 2.
Extended Correction Amount Map Generating Step
[0043] The extended correction amount map generating step is a step
of generating an extended correction amount map ECM that indicates
a correlation between the rotating speed, the load factor, and the
estimated value of the correction amount, while the opening degree
is maintained at the n-th reference opening degree and the EGR rate
is maintained at the target EGR rate. Here, the above-mentioned
basic correction amount map BCM indicates a correlation between the
rotating speed, the load factor, and the correction amount in a
region corresponding to the positive pressure region Ap in the
differential pressure map in FIG. 2. Therefore, the basic
correction amount map BCM does not indicate a correlation between
the rotating speed, the load factor, and the correction amount in
the region corresponding to the negative pressure region Am.
Accordingly, an extended correction amount map ECM is generated as
a map indicating a correlation between the rotating speed, the load
factor, and the correction amount in the region corresponding to
the negative pressure region Am. Here, since the correction amount
is not obtained in the negative pressure region Am, in the extended
correction amount map ECM, an estimated value of the correction
amount is used instead of the correction amount. The estimated
value of the correction amount is acquired by, on the basis of a
trend in the distribution of the correction amounts contained in
the basic correction amount map BCM, estimating the distribution of
correction amounts not contained in the basic correction amount map
BCM.
[0044] FIG. 4 is a diagram showing a basic correction amount map
indicating a correlation between a rotating speed, a load factor,
and a correction amount while an opening degree is maintained at an
n-th reference opening degree and an EGR rate is maintained at a
target EGR rate. The extended correction amount map generating step
generates an extended correction amount map ECM that fills the
uncorrectable region Anc, on the basis of the basic correction
amount map BCM in FIG. 3. In FIG. 4, for each of mutually different
combinations of the rotating speed and the load factor, an
estimated value of the correction amount is shown that corresponds
to the rotating speed and the load factor. In FIG. 4, each
estimated correction amount data set SCe indicates a set of data
consisting of the rotating speed, the load factor, and the
estimated value of the correction amount, which is specified by one
of mutually different combinations of the rotating speed and the
load factor.
[0045] For example, the estimated value of the correction amount is
acquired as follows. In FIG. 3, the isopleth line is set up for
each correction amount of certain value and the difference of
correction amounts between adjacent isopleth lines is (0.2C).
Therefore, distribution of the isopleth lines in the uncorrectable
region Anc can be estimated on the basis of the trend in the
distribution of the isopleth lines shown by solid lines. In FIG. 3,
estimated isopleth lines are shown by the two-dot chain lines. As a
result, the estimated value of the correction amount in the
uncorrectable region Anc is acquired and then the extended
correction amount map ECM is generated. Alternatively, by a curve
fitting method based on the correction amount data set SC, a
function may be generated in which the rotating speed and the load
factor serve as independent variables and the correction amount
serves as a dependent variable. Then, on the basis of this
function, the estimated value of the correction amount in the
uncorrectable region Anc may be acquired.
[0046] The correction amount map CM shown in FIG. 4 is generated by
combining the basic correction amount map BCM and the extended
correction amount map ECM. Since the basic correction amount map
BCM and the extended correction amount map ECM are set up for each
reference opening degree, the correction amount map CM also is set
up for each reference opening degree. Therefore, the control unit
20 stores a plurality of correction amount maps CM for mutually
different reference opening degrees.
[0047] The correction amount determination method according to the
present embodiment can specify the correction amount on the basis
of the estimated value of the correction value. Therefore, even in
operating condition that a correction value is not obtained, a
correction amount of the opening degree of the EGR valve 12 can be
determined such that the EGR rate is maintained at constant. Here,
the operating condition indicates a state specified by the rotating
speed and the load factor, and indicates, for example, the
magnitude of differential pressure.
[0048] A method of controlling the opening degree of the EGR valve
is described below with reference to FIG. 5. The method of
controlling the opening degree of the EGR valve specifies the
correction amount of the opening degree corresponding to the
operating condition, on the basis of a plurality of correction
amount maps SM obtained by the method of determining the correction
amount of the opening degree of the EGR valve, and controls the
opening degree such that the EGR rate is maintained at
constant.
[0049] The method of controlling the opening degree of the EGR
valve includes a rotating speed detection step, a load factor
detection step, an air intake amount detection step, a correction
amount map specifying step, and an opening degree controlling
step.
[0050] FIG. 5 is a block diagram showing a configuration related to
control of an opening degree. In FIG. 5, the control unit 20
includes a load factor detection section 201, a correction amount
specifying section 202, and an opening degree control section
203.
[0051] In the rotating speed detection step, the rotating speed
sensor (the rotating speed detection section) 21 detects the
rotating speed of the engine 1.
[0052] In the load factor detection step, the load factor detection
section 201 detects the load factor on the basis of the fuel
injection amount instructed to the common rail 10. As described
above, the control unit 20 changes the command value of the fuel
injection amount in accordance with changing of the load so as to
control the engine 1 such that the rotating speed is maintained at
constant. Therefore, the control unit 20 can recognize changing of
the load on the basis of changing of the command value of the fuel
injection amount.
[0053] In the air intake amount detection step, the air flow meter
(the air intake amount detection section) 22 detects the mixed
intake amount passing through the intake pipe 6. Here, as described
above, the mixed intake amount is the total amount of the air
intake amount and the EGR gas. Therefore, the air intake amount can
be specified on the basis of the mixed intake quantity and the EGR
gas.
[0054] In the correction amount specifying step, the correction
amount specifying section 202 specifies the correction amount
corresponding to the reference opening degree, the rotating speed,
and the load factor on the basis of the plurality of correction
amount maps CM. The correction amount specifying step is composed
of two steps of processing. In the first phase, among the plurality
of correction amount maps CM, the correction amount specifying
section 202 specifies a correction amount map for a reference
opening degree closest to the present value of the opening degree.
Here, the control unit 20 generates the command value of the
opening degree and then, on the basis of the command value, the
opening degree of the EGR valve 12 is controlled. That is, the
present value of the opening degree is the opening degree before
correction and indicates the command value of the opening degree at
present. For example, when the present value of the opening degree
is 35%, a reference opening degree closest to the present value of
the opening degree is 40% which is the third reference opening
degree among the first to the sixth reference opening degree. In
this case, the correction amount map CM corresponding to the third
reference opening degree is specified. In the second phase, the
correction amount specifying section 202 specifies a correction
amount corresponding to the rotating speed and the load factor on
the basis of the specified correction amount map CM. Here, the
rotating speed and the load factor used for specifying the
correction amount are the rotating speed and the load factor
detected in the rotating speed detection step and the load factor
detection step.
[0055] In the opening degree controlling step, the opening degree
control section 203 controls the opening degree to the target
opening degree corresponding to the correction amount and the
reference opening degree having been specified. As shown in the
above-mentioned Formula (4), the target opening degree is the sum
of the reference opening degree and the correction amount. As such,
the opening degree of the EGR valve is corrected such that the EGR
rate is maintained at constant.
[0056] In the method of controlling the opening degree of the EGR
valve according to the present embodiment, even in operating
condition where the correction value is not obtained, the opening
degree of the EGR valve can be corrected such that the EGR rate is
maintained at constant.
REFERENCE SIGNS LIST
[0057] 1 Engine
[0058] 12 EGR valve
[0059] 20 Control unit
[0060] 21 Rotating speed sensor (rotating speed detection
section)
[0061] 22 Air flow meter (air intake amount detection section)
[0062] 201 Load factor detection section
[0063] 202 Correction amount specifying section
[0064] 203 Opening degree control section
[0065] BCM Basic correction amount map
[0066] ECM Extension correction amount map
[0067] Anc Uncorrectable region
* * * * *